1. Field of the Invention
The present invention relates to water/wastewater treatment sludge removal systems, and more particularly, to a new and improved suction header for use with a water/wastewater treatment clarifier/thickener system.
2. Background of the Invention
Municipal water/wastewater treatment facilities treat water or wastewater in order to produce and then distribute potable water and to dispose of the industrial and municipal wastes contained in the water being treated. The amount of impurities in any particular raw water or raw sewage stream determines the amount of treatment that is required for such water or stream and is usually measured either by the amount of suspended solids or the biochemical oxygen demand. The treatment of water/sewage is typically divided into primary or physical treatment, secondary or biochemical treatment, and tertiary treatment. Improvements in any of these stages of treatment can dramatically affect the results obtained by the overall treatment.
The primary or physical treatment of water/sewage involves the removal of "settleable" solids. Fine particles tend to agglomerate so that they increase in size and settle to the bottom of a tank or the like that is a part of the treatment facility. In this regard, the coagulation of fine particles results in larger particles being formed mainly by flocculation. These larger particles are then removed by sedimentation. The total process is a clarification or thickening operation with the removed sediment often referred to as waste sludge. In its most basic form, a clarifier/thickener unit is used to decant liquid waste from any solid sludge.
In connection with such clarifier/thickener units, the waste sludge that settles to the bottom of the unit needs to be collected and removed. One way such solids can be removed from those units is with vacuum sludge collectors. Such collectors generally comprise a suction header which is rotated, slid, or otherwise translated or moved along the bottom of the clarifier unit, during which movement solids are removed without decanting or dewatering. In U.S. Pat. No. 5,772,885, issued on Jun. 30, 1998 to the inventor of the present application, a vacuum sludge removal unit is disclosed. As is described in the '885 patent, the vacuum sludge removal unit includes a sludge removal suction header with a generally triangular cross sectional shape so that a relatively large header in the cross sectional dimension is provided. With the suction header having a large width-to-height-above-ground ratio, "ground effects" are created during movement of the header across the bottom of the clarifier unit that results in the lowering of the pressure under the header (near the inlet holes through which the waste sludge is vacuumed into the header) and in improving the suction of solids during the movement of the header. Such a sludge collector allows more sludge to pass under the header in each translation of the header across the bottom surface so that more sludge is removed per each translation of the header. Otherwise, the installation of headers need to be very close to the bottom of the unit to avoid excessive amounts of cleaner water being removed from above the header due to gravity.
The particular triangular cross sectional shape of the header with an obtuse angle at the top or apex of the header results in a lower projected area of the header as it is being translated across sludge in the clarifier unit. This tends to minimizes the resistance of the header as it moves within the liquid in the clarifier unit and also the header tends to cause less turbulence of the liquid as it is being translated within the clarifier unit. By minimizing such turbulence, the sludge remains settled (undisturbed) as the header passes over the sludge such that any interference with the suction's flow lines is minimized. In addition, the water coming from above the header is forced to separate from the header at the edges of the triangle. Consequently, the fluid has to travel a longer distance before reaching the suction inlet holes that are located underneath the header so that the zone where the waste sludge is influenced is increased. In fact, the mixing of fluid and sludge under the header tends to fluidize the sludge, and in combination with a low pressure around the suction inlet holes, aids in urging the fluidized sludge into the inlet holes. The triangular shape of the header of the '885 patent also provides a header with improved physical rigidity, especially in the direction of translation of the header, so that bowing of the header is minimized and the risk of damage to the header is decreased when the header encounters areas of thick sludge or other obstacles.
Another feature described in the '885 patent relates to equalizing the pressure distribution within the header. With a more uniform pressure distribution within the header, the flow distribution across all of the inlet holes (especially those holes at the end of the header which are furthest away from the vacuum source) is more uniform. In order to so equalize the pressure distribution, internal annular passages are disposed along the intersections of the outer walls of the header for equalizing the pressure distribution inside the header.
The particular cross sectional shape of the header member disclosed in the '885 patent improves the performance of the sludge removal system disclosed in that patent and the internal annular passages tend to equalize the pressure distribution inside the header member. However, the performance of a sludge removal system of the type disclosed in the '885 patent can be further improved by reconfiguring the cross sectional shape of the header member and the pressure distribution within the header member can be further improved by redesigning the distribution of the vacuum within the header member.
Accordingly, it is an object of the present invention to provide a new and improved sludge removal suction header for use with a municipal water/wastewater clarifier/settling system.
It is another object of the present invention to provide a new and improved sludge removal suction header for use with a municipal water/wastewater clarifier/settling system wherein the cross sectional shape of the header provides improved performance.
It is still another object of the present invention to provide a new and improved sludge removal suction header for use with a municipal water/wastewater clarifier/settling system wherein the cross sectional shape of the header has a generally convex or curved top section having overhanging wings extending below the bottom wall of the header.
It is yet another object of the present invention to provide a new and improved sludge removal suction header for use with a municipal water/wastewater clarifier/settling system having baffles within the header to equalize the pressure distribution within the header.